The present invention pertains to a measuring circuit, and more particularly to a measuring circuit for measuring a frequency of an input signal and for displaying it on a display apparatus.
Various measuring apparatuses are in use for controlling an operational status of a machine. Many of these apparatuses utilize a sensor for generating an electric signal of a certain frequency so as to perform a measurement of an operating speed or a speed of revolution, for example, of a machine. The above sensor is so configured as to display the measurement result on a display apparatus.
Apparatuses such as a speedometer of an automobile or a revolution indicator of an engine convert a frequency of an input signal from a sensor to an analog or digital indicated value by a measuring circuit, and display the value on a display apparatus.
Measuring circuits designed for supplying a signal to a display apparatus in response to a frequency of an input signal include circuits for counting the number of cycles in a predetermined period of time and converting the count into a frequency; also included are measuring circuits equipped with a function of measuring a time of one cycle and converting said time into a frequency. Another such circuit is known that converts a frequency directly into a voltage signal by using a frequency/voltage (F/V) converter.
FIG. 1 is a block diagram describing an example of a conventional frequency measuring/displaying apparatus 200. A detection pulse signal 201 from a speedometer or a revolution indicator and reference clock pulses 203 from clock pulse generating means 202 are input into a cycle detecting means 204. The cycle detecting means 204 detects a cycle T of the detection pulse signal by counting the number of reference clock pulses corresponding to a cycle of a detection pulse signal. Arithmetic means 206 not only calculates a frequency 1/T on the basis of a signal 205 having a cycle T but also determines by calculation an output 209 to be sent to a display apparatus driving means 210 on the basis of a parameter 208 supplied from a memory 207. The display apparatus driving means 210 converts the digital output signal 209 into a signal appropriate for the purpose of driving a display apparatus 212 to which a driving signal 211 is output.
However, the above-mentioned conventional measuring apparatus has a disadvantage in that it requires complex circuit construction and computation for mathematical division operations, it is required when detecting a frequency of a detection pulse signal, to first calculate a cycle T and then convert it to a frequency 1/T. Further, the characteristics of a display apparatus designed for analog display often exhibit dispersion, which is extremely difficult to correct and is an obstacle to accurate display.
Conventionally, when there is a need for a display of a plurality of measured values, such as in the case of a speedometer and a revolution indicator above, a normal practise is that a measuring circuit processes frequency signals corresponding to each measured value given, and various arithmetic operations are subsequently performed in correspondence with characteristics of each display apparatus before an output is sent to a display apparatus. Accordingly, when display apparatuses of both a speedometer and a revolution indicator are driven, measuring circuits are provided independently, one for a speedometer and one for a revolution indicator.
Such a configuration, in which a plurality of measuring circuits for driving a plurality of display apparatuses are required, brings about a large circuit scale and a rise in production cost. Hence a need for a measuring circuit having a simple circuit configuration capable of driving a plurality of display apparatuses with a single circuit.